Finite Element Analysis Of Engine Exhaust Manifold Based On Fluid-solid Coupling

With development of engine technology,stringent emission regulations and continuous high demanded of power improvement,the effective pressure in cylinder and combustion temperature is increasing higher and higher.The high pressure and temperature lead the heat load of manifold close to its limit.The exhaust manifold is affected by heat load,vibration load,air flow and material properties,etc..This paper selected a six cylinder diesel engine as the research object.In the reliability test,exhaust manifold cracked.Predict the mechanical strength of thermal load for fatigue life by the method of simulation analysis.And investigate whether the cracking of the exhaust manifold is caused by resonance.First,built the model of the exhaust manifold by using three-dimensional CAD software Pro-E.Secondly,import the part model into the three-dimensional CFD software Fire,and establish the inner surface of the exhaust manifold as the three-dimensional flow field analysis model.Obtain the boundary conditions of heat transfer inside the exhaust manifold by analyzing the flow field in the exhaust manifold.Thirdly convert the exhaust manifold model to the finite element analysis software ABAQUS.Apply the thermal boundary conditions to the finite element which get from the CFD model.Analysis heat transfer analysis and thermal stress of the wall of the exhaust manifold.Estimat the fatigue life of the exhaust manifold which is based on the thermal stress analysis using ManSon-Coffon formula.Finally,analysis the finite element model is performed to determine whether the failure of the exhaust manifold is affected by the resonance by modal analysis.Through this study,the cracking of exhaust manifold in reliability test is caused by thermal stress and exhaust temperature constraints.The natural frequency of the seven order modes of the exhaust manifold and the natural frequency of the eight mode natural frequency are in the range of the engine's fundamental frequency.Cracking failure in the non-stress concentration part is affected by the engine resonance.The plastic strain caused by the heat load of the exhaust manifold could be avoided by improving the structure of the exhaust manifold.So as to avoid the fatigue damage of the exhaust manifold.The vibration damage on the exhaust manifold caused by the rotation of engine could be effectively avoided by changing the material and constraint conditions of the exhaust manifold.